A white tiger mauled to death a school student in a New Delhi zoo on Tuesday, an official and a witness said.

Television channels broadcast closed-circuit footage of the frightened boy inside the tiger's enclosure in the zoo that houses six white tigers, along with lions and panthers.

"We are all in a complete state of shock," said Amitabh Agnihotri, the director of the National Zoological Park in the Indian capital, adding that the body was being sent for a post-mortem examination.

"The tiger grabbed the youth and killed him. I am not clear whether the youth jumped into the cage or he slipped accidentally."

Authorities have yet to ascertain whether the student was alone or accompanied by friends.

"The barricade was too low and it seems the tiger grabbed the youth into his cage and firmly latched on to the youth's neck," an eyewitness who alerted the police told an Indian news channel.

"We tried to throw sticks and stones at the tiger but we could not save the youth," he said, adding that the tiger killed him in less than 10 minutes.

An eyewitness who filmed the incident said, "the boy was begging for his life for at least 10 to 15 minutes."

In 2000 a tiger mauled a man in a zoo in the eastern state of West Bengal.

In 2011, India had 1,706 tigers, or more than half the world's population of the endangered species.